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Nonlinear Hall Quantum Oscillations to Probe Topological Brown-Zak Fermions in Graphene Moiré Systems
Jinrui Zhong1, Huimin Peng1, Yuqing Hu1
1Beijing Institute of Technology, Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), School of Physics, Beijing 100086, China.
Physical Review Letters
|July 7, 2026
Summary
Researchers discovered new quantum oscillations in the nonlinear Hall effect (NLHE) within graphene moiré systems. This finding enables sensitive detection of Brown-Zak fermions and reveals their topological nature.
Area of Science:
- Condensed Matter Physics
- Quantum Materials
- Solid-State Physics
Background:
- The second-order nonlinear Hall effect (NLHE) is linked to the quantum geometry of Bloch wave functions.
- Research on NLHE under magnetic fields is limited, despite the utility of quantum oscillations in linear response studies.
- Exploring quantum oscillations in NLHE could unveil new quantum geometric properties of quasiparticles.
Purpose of the Study:
- To propose and experimentally investigate a novel type of quantum oscillations in the nonlinear Hall effect.
- To explore the quantum geometric properties of novel quasiparticles, specifically Brown-Zak fermions.
- To detect the topological nature of Brown-Zak fermions.
Main Methods:
- Experimental probing of nonlinear Hall effect quantum oscillations in graphene moiré systems.
- Applying magnetic fields to observe recurring Bloch states and alternating NLHE mechanisms.
- Analyzing nonlinear transport under commensurability conditions.
Main Results:
- A new type of nonlinear Hall effect quantum oscillations was observed.
- Sensitive detection of Brown-Zak fermions was achieved with a low onset field (0.5 T).
- Quantum geometric contributions were identified as the primary driver of nonlinear transport for Brown-Zak fermions under specific conditions.
Conclusions:
- The study establishes a new class of quantum oscillations.
- It provides the first experimental evidence for the topological nature of Brown-Zak fermions.
- The findings open new avenues for exploring topological quasiparticles.
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